I would still use the clamps in the areas you can get them in. If you had more than a 1/32 inch gap in the sheeted areas, I would be suprised and look at the trueness of the root ribs before glueing. The small gap would be filled with epoxy and serve the purpose. The tape method mentioned is still advisable with the adition of your clamps. Is the rest of the center section suposed to be sheeted after the wings are joined? I would guess, yes. You can always glass the center section as well if the whole center section will be sheeted.